Cross Multiplication Calculato

A simple application which allows users to calculate cross multiplications in their daily activities. It allows users to find the equivalent of figures given previous values. It has 4 text boxes, the first 2 gives the user the opportunity to provide a previous figure and its subsequent result. The third text box allow you to input a new figure and generates the new result in the 4th box based on the first result from the second box.
For example : If a user makes 100 dollars in 2 days and wants to know how much they will make in 23 days, from the app input : enter in first box [100], second box [2], and then third box [23]. The application will automatically generate the result in the fourth box for the user.